The present invention relates to subsea wellhead orientation, and more particularly, in certain embodiments, to methods and systems for aligning a Christmas tree with a tubing hanger.
Tubing hangers need a specific orientation with respect to the wellhead because they contain numerous bores, which require alignment with corresponding portions of respective Christmas trees. Conventionally, there are two ways to achieve orientation of a Christmas tree relative to a tubing hanger. The first uses a tubing spool assembly, which latches to the wellhead and provides landing and orientation features. The tubing spool is very expensive and adds height to the overall stack-up. Additionally, the tubing spool is so heavy that very few work class vessels can install it, and it frequently requires installation by expensive drilling vessels. Furthermore, the drilling riser must be removed to install the tubing spool.
The second method of orienting a Christmas tree relative to a tubing hanger involves the use of a blowout preventer (“BOP”) stack hydraulic pin and orientation adapter joint. This method requires detailed knowledge of the particular BOP stack in order to accurately install a hydraulically actuated pin, which protrudes into the BOP stack bore. An orientation helix is attached above the tubing hanger running tool, and, as the tubing hanger lands, the helix engages the hydraulic pin and orientates the tubing bores to a defined direction. This method requires accurate drawings of the BOP stack elevations and spacing between the main bore and the outlet flanges, which may require hours of surveying and multiple trips to make measurements. Tremendous room for error exists with this method, particularly in older rigs. Thus, this method requires significant up front planning. Additionally, setting the lockdown sleeve in the wellhead generally requires a rig because the BOP must remain in place as a reference point for orientation of the tubing hanger and corresponding lockdown sleeve.